Grinding machine



Feb. 2, 1943. PQORMAN 2,309,668

GRINDING MACHINE Filed Nov. 10, 1941 v 6 Sheets-Sheet 1 Feb, 2, 1943. J. E. POORMAN 2,309,668

I GRINDING umcanm Filed Nov. 10, 1941 a Sheets-Sheet 2 Feb. 2, 1943. J. E. POORMAN 2,

GRINDING MACHINE Filed Nov. 10, 1941 6 Sheets-Sheetfi mini Feb. 2, 1943.

J; E. POORMAN GRINDING MACHINE Filed Nov, 10, 1941 6 Sheets-Sheet 4 l l llg ljglllIlllllilllllli lliln'" F I i I lllllllllllll Feb. 2, 1943. J. E. PooRMAN GRINDING MACHINE Filed Nov. 10, 1941 6 Sheets-Sheet 5 F 1943- J. E. POORMAN a09,68

GRINDING MACHINE Filed Nov. 10,1941 I e Sheets-:Sheet 6 TABLE MOVEM'A/T a:

Patented Feb. 2, 1943 UNITED STATES PATENT OFFICE GRINDING' MACHINE John E. Poorman, Philadelphia, Pa. Application November 10, 1941, Serial No. 418,569

27 Claims. (01. 51-231) This invention is directed to an improvement in grinding machines, with particular view of controlling the mechanism to insure absolute and desired precision in grinding operation.

In conventional grinding machines, it is customary to provide for automatic operation after the setting of the machine for the desired grinding. Thus in such conventional machines the table or other material base is set for a predetermined limited movement for the desired grinding and during the final step of this movement mechanism is set in motion to reverse the operation of the drive for the return of the table, and, if desired, a further grinding during such return. It not infrequently happens that there is a variation in motion between the tim the automatic reversing mechanism commences to up erate and the completion of that operation, which variation is not infrequently due to inaccurate timing, Wear of parts, or momentum over-run. Any such variation is, of course, highly undesirable in any grinding operation and absolutely vital in precision grinding.

The primary object of the present invention is to insure an absolute predetermined stop for the movement of the table at the desired point, while at the same time permitting a control and operation of the table reversing mechanism, in order to insure that the cessation of the grinding operation can be positively controlled with extrem precision and provide that the reversing mechanism while set in motion incident to the stop of the table, may nevertheless proceed to carry out its reversing function without the possibility of any table movement, and therefore of any grinding, beyond the absolute predetermined limit.

A further object of the invention is the provision of means whereby through a simple mechanical adjustment the machine may be converted to a more or less conventional grinding machine wherein the movement of the table in the grinding operation continues substantially to and including the point of power reversal, thus materially increasing the commercial value and adaptability of the machine.

A further object of the invention is the pro-- vision of means whereby the machine may, at will, be disconnected from the power drive and operated by hand under any condition or conditions requiring such operation. While this hand control is more or less conventional in machines of this type, the mechanism for effecting it in the present machine is coordinated with the mechanism of the machine as a whole and constitutes a radical necessity in the present specificimprovement.

The invention is illustrated in the accompanying drawings, in which machine below the table, parts being shown in elevation.

Figure 4 is a diagrammatic view with parts distorted for purposes ofclearness illustrating the reversing mechanism detail for correlated 4 positions. 7

Figure 5 is a broken transverse section partly in elevation illustrating particularly the hand operated mechanism.

Figure 6 is an enlarged sectional view partly in elevation of the hand operated mechanism for themachine.

Figure 7 is a view in elevation of the gear arrangement for selectively controlling the direction of table drive from the power means.

Figure 8 indicates separate views of the means for interrupting the power drive of the table to permit manual control.

Figure 9 is a view in section partly in elevation showing the upper and lower stops for the table and the means for controlling the stops.

Figure 10 is a sectional view partly in elevation of the power controlled element for operating the reversing mechanism.

Figure 11 is a'horizontal sectional view part I ly in elevation of the same.

Figure 12 is a viewin section partly in elevation of the gear connection between the reversing lever and reversing shaft.

Figure 12A is a diagrammatic view showing the relation of the parts when the table is in the arrow-indicated direction and before the table is stopped.

Figure 123 is a similar view showing the relation of the parts following stopping of the table.

Figures 13 and 14 are perspective views of modified forms of gearing and stopping mechanism.

The grinding machine of the present invention is generally, aside from the details to be de scribed, of more or less conventional form, and

while it is necessary to describe some of such conventional parts for a. complete understanding of the invention, it is to be understood that the invention is, with permissible mechanical changes, adapted for any grinding machine of l the 7 type.

The machine comprises a main frame I of any appropriate structure on which is mounted a table 2 for receiving material to be operated on by the grinding mechanism, illustrated conventionally at 3. The grinding mechanism may be of any appropriate construction, such for example, as shown in Patent No. 1,096,188. The lower sur face of the table is formed near its rear edge a with a V-shaped rib 4 to slidably seat in a similarly formed guideway 5 in the frame. The forward edge of the table has a bearingplate 6 to slide upon an appropriate area I of the frame. The table has a central depending rib 8 on which is formed or secured a rack bar 9 through which the table is reciprocally moved on the frame.

The forward edge of the table 2 is provided with a hollow guide bar l rigidly secured to the table and having a comparatively narrow opening H mounted in the guide bar ID are two heads l2, having guide blocks l3 conforming to and slidably mounted in the guide bar l0 and adapted to be fixed and thereby to fix the heads' [2. in any relative positions longitudinally of the guide bar by set screws M. The heads proper bear against the outer surface of the guide bar and are each formed at their upper ends at points above the guide bar for the reception of threaded stops extending in parallelism to the plane of movement of the table 2.

Supported upon the frame I is a bracket l6 including at its forward end upstanding spaced arms I1 which, as shown in Figure 1, extend upwardly above the guide bar and forwardly and in spaced relation to the heads l2. Swingingly supported on a cross bar at the upper end of the arms I! is a stop bar l8, which when in normal operative position is in the path of movement of the stops l5. The stop I8 is provided with a rearward extension l9 formed at its rear'end with a circular depression 20, in which is threaded a handle 21. The stop I8 which rests upon the cross bar at the upper end of the arm I'I when in normal position, may obviously be swung out of that position by downward pressure of the handle 2|. r

A reversing shaft 22 extends transverse the frame and at its forward end which is below the bracket l6 and centrally of the plane of the arms I! is provided with a gear connected reversing lever 23. The lever is, of course, loose onthe shaft to be removable at will but is designed, of course, to correspondingly operate the reversing shaft in any movement of the lever. The upper end of the lever 23 is formed with a vertical socket 24 in which is slidably mounted an auxiliary stop 25. The stop is provided with-a pin 26 leading through a slot 21- in one wall of the lever and provided beyond the lever with a fitting 28 from which extends a rod 28, the upper end of which terminates in a ball 30 arranged within the depression 20, and more particularly within the hollowed lower end 3| of the handle 2 I. The hollow in the handle has its upper wall spaced a distance from the ball as to permit the handle to move the stop- I8 to a position free of the path of movement of the stops l5, without engaging or contacting with the ball 30. Further movement of the handle downward will engage the ball and correspondingly move the arm 29 and the stop 25 to inoperative position. When the stoplB is in operative position, the ball 30 is in contact with the bottom wall of the depression 20, and the stop 25 is, therefore, also in operative position. However, the operator may, at will, shift the stop l8 out of operative cothrough its forward. wall. Slidably operation with the stops l5, leaving the stop 25 in operative position, or may continue downward movement of the handle and so move both stops out of operative position.

As stated, the stop I8 is, when in operative position, in the path of movement of the stops l5 which, of course, are moved by and with the table 2, and are adjustable in any desired position lengthwise of the table. Therefore, the table will be brought to absolute rest when the particular stop 15 according to the direction of table movement engages the stop Hi. This interruption of table movement is utilized in connection with the improvements to which the present invention is more particularly and directly concerned. That is, wherein the table is brought to rest at a predetermined point in its movement and the direct means for reversing the drive of the table is brought into operation following the complete cessation of table movement.

The stop 25, however, is designed to provide the operating instrumentality wherein the machine may be selectively adapted to permit movement of the table up to and including the reversal of the table drive. The stop 25 is positioned in the path of movement of depending lugs 32 on the blocks I2, and it is, of course, apparent that if the stop I8 is in operative position, the stop 25 cannot function. The reversing mechanism controlled by the reversing lever 23 will be more specifically described hereafter.

The power shaft 33 mounted in suitable bearing at the rear of the frame i designed to be continuously operated in one direction. .Spaced pinions 34 and 35 are mounted loosely in spaced relation on the power shaft and provided with clutch faces 36 with either of which an intermediate clutch member 31 is slidably mounted or otherwise fixed to the power shaft and is adapted to engage. The pinions 34 and 35 cooperate with a bevel gear 38 fixed on a transverse shaft 39 extended to and mounted in the frame I. On the shaft within the frame I is a loose gear 46 which may be fixed with relation to the shaft 39 or free of shaft rotation through the medium of a control clutch assembly indicated at 4! and hereinafter more particularly described. The pinion 40 cooperates with a gear 42 mounted upon a stub shaft 43 supported in the frame I, which stub shaft carries a gear 44 cooperating with the gear 45 on a second stub shaft 46, which gear 45 operates through the automatic reversing mechanism to be later described and indicated generally at 41 to operate the gear 48 on the shaft 46, which gear 48 cooperates directly with the rack 9 of the table 2.

The automatic reversing element 41, illustrated I more particularly in Figures 10 and 11, is in the nature of a differential control responsive in its movement to the interruption of movement of the table 2 during the continued operation of the drive shaft. This reversing mechanism includes a block 50, and is supported on the shaft 46. The respective ends of the block are provided with beve1 pinions 5| and 52 which cooperate at diametrically opposite points with bevel gears 53 and 54. The bevel gears cooperate with the pinions at diametrically opposite points of the latter, and the bevel gear 53 is carried by the spur gear 45, while the bevel wheel 54 is carried by the spur gear 48. A bar 55 is secured to the upper surface of the block and extends in both directions beyond the ends of the block. One end of the bar is connected by a swinging link 56 to an arm 51 rigidly connected to the reversing shaft 22. The opposite end of the bar is connected by a swingingly connected block 58 to a threaded shaft 59 which extends through a block 68 swiveled at 6| to a fixed part of the frame. Stops 62 and 63 are threaded for adjustment on the shaft 59 above and below the block 60, and springs 64, of a character to present a substantial pressure when compressed, are arrangedbetwee the block 60 and the stop 62 and 63.

The means for automatically shifting and locks ing the sliding clutch element 31 on the power shaft includes a lever 65 pivotally mounted at its lower end at 66 on a U-shaped member 61 mounted in the frame in substantial alignment with the power shaft 33 and is formed above the pivot 66 with an offset 68 connected by-an arm 69 to the reversing shaft 22, the arm forming a rigid connection with the shaft. The upper end of the lever 66 is formed with a transversely arranged trip plate 18, the upper end of which is of curved or arcuate form. A shifting rod 1| is connected at one end to ashift lever 12 cooperating in the usual manner with the movable member 31 of the power shaft clutch. This rod 1| is slidably mounted in the upright arms of the frame support 61 and is provided with spaced block 13-14 rigidly secured to the rod. Trip rods 15-16 are pivotally supported at the upper ends of the U- frame 61 and overlie and bear on the respective blocks 13 and 14. Each trip rod is formed with a depending lug 11 adapted to cooperate with the adjacent blocks 13 and 14, when the particular trip rod, which moves downward by gravity, is in its lowermost position. The lever 65 is provided with a sleeve 18 swiveled through'which sleeve the rod 1| is slidably mounted, and between the respective ends of the sleeve 18 and theblocks 13 and 14 are arranged springs 19 whichencircle the rod 1|.

The clutch shifter and locking mechanism described is controlled and operated in response to the movement of the reversing shaft 22. As this shaft is turned in one direction, as in the direction of arrow A, the lever 65 is shifted in the same direction toward the right in Figure 4 and its upper arcuate end will ride under the appropriate bent end of the trip rods 16, for example, and at the same time exert pressure on the spring 19 against the block 14. As the end 10 of the lever 65 rides beneath the trip rod 15, the latter is raised, releasing block 14, and freeing the blockheld end of the tensioned spring 19. This moves the rod 1| to shift the movable clutch member into clutching cooperation with, in the instance described, the pinion 35 on the power shaft to drive the train between the power shaft and table in one direction. Incident to this shifting movement, the opposite block 14 on the rod 1| is moved to a position to permit the cooperating trip rod 15 to drop to a position to cause the lug 11 thereof to engage behind the block 13, thus locking the rod 1| and. movable clutch member controlled thereby in predetermined clutching relation. Under the opposite movement of the re- Versing shaft 22, the lever 65 is swung in the opposite direction. In this movement the arcuate end 18 rides beneath the trip rod 15 and releases the block 13 from the lug 11, then continues to exert pressure on the spring 19 and move the rod 1| to shift the movable clutch member 31 into cooperation with the clutch 36 of the pinion 34, thus reversing the effect of the power shaft on the gear train intermediate that shaft and the table 2. In this movement the block 14 is moved to a position to permit the lever 16, now free of the 75 arcuate head 10 of the lever 65 to drop and cause the lug 11 thereon to lock behind the block 14 and hold the sliding clutch in its then set position, as shown in Figure 4.

The differential described is directly operated by the power mechanism. It willbe noted that when one of the stops I5 engages the stop |8 in the power driven movement of the table 2, the table is brought to an absolute stop at an exact predetermined point. Incident to this cessation of movement in the table, the driving pinion 46 for actuating the table will also be brought to rest. This stops the movement of the bevel gear 54 .of the differential and by fixing this gear,

will cause the pinions 5| and 52 to travel in opposite directions over bevel gear 54 by reason of the movement of the bevel gear 53 which is being driven by the power shaft through the gear train described. As the pinions 52 and 52 are mounted in the block 50, the described movement will cause the block to tip, in one direction or the other, according to power drive, correspondingly moving the bar 55 and rocking the power shaft 22 to effect movement of the clutch shifting and 5locking mechanism described. This movement of the block and bar 55 acts to compress either the upper or lower spring 64 according to direction of movement, and cause the compressed spring to return the block 58 and bar 55 to a normal horizontal position as soon as the drive is completed through the pinion 48, the pinions 5| and 52 rolling with respect to the previously fixed bevel gear 54 to permit this movement of the block to normal position. The return of the block to normal position will obviously return the lever 65 of the clutch shifting and locking mechanism to a neutral or centered position free of cooperation with either trip lever 15 or 16.

The invention also contemplates the provision of means by which the power shaft clutch mechanism may be operated as the table reaches a final position, but before its movement is interrupted. Under these conditions, and where, for example, an exact precision grinding operation is not necessary or required, the table will be permitted to move with the material subjected to the machining operation, and the reversing of the drive for the table perfected during the final limit movement of the table and before its movement is completely interrupted. This particular mechanism hereinafter referred to as the auxiliary reversing mechanism is perfected through movement of the shifting lever 23 under the influence of the cooperation of the table carriage stop 32 and the stop 25 on the lever 23. To provide for this operation the handle 2| is moved to shift the stop |8 out of the path of either stop |5 without, however, disturbing the operative position of the stop 25. As the table moves, one of the stops 32 thereon will engage the stop 25 and swing the lever 23 in the appropriate direction. This lever 23 is mounted upon a sleeve 86 encircling the reversing shaft 22 and rotatably mounted in the frame I. The inner end of the sleeve is provided with a bevel gear 8| cooperating with a frame supporting bevel gear 82 which in turn cooperates with a bevel gear 83 fixed upon a sleeve 84 encircling the reversing shaft 22 and pinned to that shaft as at 85. Thus movement of the lever 23 under the influence of the moving table will cause the reversing shaft to be operated to effect the previously described operation of the clutch shifter and locking mechanism described.

From the immediately above description, it

will be apparent that theoper'ator mayse't the machine for the particularly important precision operation wherein the table is brought to absolute rest at a predetermined point and the power drive reverse completely operated following the stopping of the table, or by manually moving the stop I8 out of the path of the stops I on the table, permit the table to move to a definite stop position and effect the power drive reverse during the final movements of the table in the particular direction.

Provision is also made for manually interrupting the movement of the table at any time to permit adjustment of the table or a setting thereof at will as the particular operation may require. To this end, the shaft 39 is divided, and on one section of this shaft are clutch elements 86 arranged for selective cooperation with a movable clutch member 81 on a sleeve 39 on one section of shaft 39. The clutch 81 is operated by a shifter rod 88, connected at its lower end to a rod 89, which extends through the frame and through a sleeve 90 in the front of the frame. The rod 89 is provided with an operating handle 9|, and on the handle and sleeve 90 are provided cam members 92-93 which when the handle is turned will cause longitudinal movement of the rod 89 and so move the shifting clutch member 81. The shifter rod 88 is provided with a pin 94 seating ina recess 95 and operated by a spring 96 to move the arm 88 in a direction to connect the shifting clutch member 81 for drive from the driving shaft. Thus when the handle 9I is turned in one direction, the movable clutch mem-. ber 81 is shifted to free the pinion 40 from the influence of the driving shaft, while on the release of the handle the spring 96acts to restore the clutch to a position to cause the driving shaft to operate the pinion 40.

The shaft 39, or that end thereof carrying the pinion 40, extends beyond'the front of the frame through a sleeve 9?, and mounted-on the sleeve in advance of theframe is a handle 98 by which the end of the shaft 39 may be rotated through the medium of a disc 99 on the end of the shaft bearing against and pinned at I00 to the handle. Thus when the clutch member 81 is free of cooperation with the power driven clutch member 86 the forward portion of the shaft 39, and thereby the gear 40, and train of gear leading to and operating the table, may be turned by "the handle 98 and the table adjusted or shifted as desired. The pin I00 is designed to act as a shear pin so that in the event interruption of the drive tending to breakage is encountered under operation of the power means, the gear 40 will be freed from the influence of the driving means through the shearing of the pin I00.

It will be apparent from the above description that the table may be stopped and the grinding effect upon the material carried by that table interrupted at any particular or desired point to insure complete and absolute precision in any grinding operation. It will be further evident that it is the interruption or stopping of the table which sets in operation the reversing mechanism, and that after the table is stopped, the power means in its continued movement will bring about an effective reversal of its operative effect on the table Without in any way permitting or influencing any table movement. Thus,'

regardless of wear of parts'ordifiiculty in exact reversing period, the power means will still continue to bring into effect its own reversal after a complete cessation of table movement, and without affecting such table until complete reversal is effected.

It will, of course, be understood that the gearing train and the arrangement of the gears, except in the mounting of the difierential, may be varied at will to suit the driving requirements and operation of the table, and that the various parts herein both asto proportions and particular arrangement for cooperation may be mechanically varied to suit particular installations.

Figure 13 illustrated a modified mechanism to be used as a substitute for the differential described in the preferred form. In this particular form, the power drive, which, of course, is selectively controlled in the preferfred form, is indicated at IOI. The power gear is internally geared at I02 and mounted loosely upon a shaft I03 which also carries rigidly a pinion I 04 for cooperating with and actuating the rack 9. A tiltable plate I05 is swingingly supported at H0 on the shaft. I03 and loosely receives a superimposed shaft II I carrying at one end a pinion I I2 in cooperation with the rack pinion I04 and at the other end a pinion H3 in cooperation with the internal gear I02 of the power gear. The plate I05 is connected at one end as at II4 to the reversing shaft 22 and provided at the other end with a spring-pressed rod II 5 similar to that of the preferred form, which creates spring pressure in the plate when tilted to restore it to normal position. In this form when the gear pinion I04 is brought to rest by the stopping of the table, the shaft III is continued in motion by the power gear, the bodily movement of the pinion II2 rocking the Plate I04 in the desired direction to actuate the reversing mechanism.

In the form shown in Figure 14, the power gear I I6 is fixedly mounted upon a shaft I I! carrying a loose gear IIB for operating the table rack 9. A tiltable block H9 is loosely mounted in the shaft III and provided with means I20 to operate the reversing shaft 22 at the opposite end, with a spring-pressed rod I 2I similar to the preferred form. The power'pim'on H6 is connected to an elongated gear I22 which in turn meshes with an elongated gear I23 in cooperation with the rack pinion H8. The elongated gears I 22 and I23 are mounted upon shafts I 24 and I25 respectively which are loosely mounted in bearing sockets I26 in the tilting block II9. When the table and rack 9 are brought to rest, further movement of the gear I I8 is interrupted and. as the power gear II6 continues to operate, the elongated gears I22 and I23 will move bodily to swing the block I I9 in the desired direction to operate the reversing means.

What is claimed as new is:

1.;In agrinding apparatus including a material supporting table, grinding mechanism for operating on the material, power means for operating the table, means for completely stopping table movement, and associated mechanical elements operated by the power means following complete stoppage of the table and constituting means for reversing the effect of the power means on the table.

2. In a grinding apparatus, a material supporting table, power means for operating the table, reversing mechanism for the power means, and associated mechanical elements constituting means for controlling the reversing means by the power means while preventing any power means operating effect on the table.

3. 'In a grinding apparatus, a material supporting table, power means for driving the table in both directions, means for stopping movement of the table under the power means, means for reversing the-power means, and an element forming an essential part of the power train to the w table for actuating the reversing means, said element acting to actuate the reversing means after the operating efi'ect of the power means on the table has ceased.

4. A grinding apparatus including a material supporting table, a power train for operating the table, means for stopping movement of the table 'under the power train, reversing mechanism for the power train, and a difierential interposed as an active element in and operated by the power 'trainfollowing stopping of table movement to the reversing mechanism includes an automatic power reversing control set in operation by the differential and including an automatic lock for holding the reversing mechanism in a set position.

7. A construction as defined in claim wherein the differential includes a block inclined in response to difierential action following interruption of table movement, and means for utilizing the inclination of the block to actuate the reversing mechanism.

8. A construction as defined in claim 5 wherein the difierential includes a block, spaced bevel gears mounted in the block, one driven by the power means and the other actuating the table, and bevel pinions mounted in the block and connecting the respective bevel gears at diametricall opposite points, whereby on complete cessation of table movement one of the bevel gears is stopped while the other continues to operate under the power means to cause the bevel pinion to tilt the block.

9. A grinding apparatus including a material supporting table, a power means for operating the table in both directions, means for stopping table movement, reversing mechanism for the power means, a primary reversing mechanism control operated following cessation of table movement, a secondary reversing mechanism control operated immediately preceding cessation of table movement, and selective means for inaugurating either control at will.

10. A grindin apparatus including a mate rial supporting table, a power means for operating the table, adjustable stops for stopping movement of the table in either direction, mechanism for reversing the efi'ect of the power drive on the table, and means operative solely by the power means following the stop-controlled cessation of movement of the table to actuate the reversing mechanism.

11. A contruction as defined in claim wherein the means for actuating the reversing mechanism is set in motion by the stopping of the table movement.

12. A grinding machanism including a material supporting table, power means for operating the'table including-a train of gears, means for reversing the efiect of the power means on the train of gear, a differential included in said train of gear, means for stopping movement of the table under the power means, a connection between the difierential and the power reversing means, and means incident to and following stoppage of table movement for compelling action of the difierential through said connection to the reversing means.

13. A grinding apparatus including a material supporting table, a power means including a train of gear for operating the table in both directions, means for reversing the effect of the power primary means on the train of geartmeans forstopping the movement of the table in both directions, mechanism operated bysaid table stopping means to co'n 'ipel-the train of gear to actuate the reversing means following cessation of table movement, a secondary operating means to stop table movement in either direction and actuate the reversing mechanism prior to complete cessationof table movement, the primary and secondarytable-stopping means being selective for operation at will. 14. A construction as defined in claim 12 including selective means for operating the reversing mechanism and stopping table movement in a concurrent operation. 4

15. A construction as defined inclaim 12 in eluding a stop for stopping the table'movement prior to the operation of the reversing mechanism, a second stop for operating the reversing mechanism during table movement, and manually operable means for selectively controlling the stops in their eifect on table movement.

16. In a grinding 'apparatus'a material supporting table, powermeans including a train of gear'for operating the table in both directions, reversing means for thepower means,'adjustable stops for stopping movement of the table, adifferential included in the train of gear, said differential being operated to actuate the reversing mechanism by the power means and following the cessation of table movement.

17. A construction as defined in claim 16 wherein the reversing mechanism includes a means for directly actuating reverse control and locking said control in operative position.

18. In a grinding apparatus, a material sup porting table, power means for driving the table in both directions, adjustable stops carried by and movable with the table, means to be engaged by said stops in the movement of the table to stop the table against further movement beyond a point selected by the particular stop, means for reversing the power means in its effect on table movement, and a difierential connected to and operating the reversing mechanism under the influence of the power means following the table movement cessation by either of said stops.

19. In a grinding apparatus, a frame, a material supporting table slidable on the frame, continuously operating power means for operating the table, adjustable stops carried by the table, a member carried by the frame to be engaged by a particular stop according to the direction of table movement to stop the table, and a dinerential connected to the reversing mechanism and set in operation to actuate the reversing mechanism following stoppage of the table through cooperation of the table-carried stop and said member.

20. In a grinding apparatus, a frame, a materia1 suporting table movable on the frame, power means for operating the table, reversing mechanism for the power means, adjustable stops carried by the table and each including a primary stop element and a secondary stop element, a primary member carried by the frame and movable to a position in the path of movement of the primary stop elements of the stops or out of said path at will, a secondary stop member carried by the frame and in the path of movement of the secondary stop elements of the stops, a shaft for actuating the reversing mechanism, means for operating the shaft in cooperation of the secondary stop element and the secondary member, and a differential movable by the power means following cooperation of the primary stop element of the stop and the primary cooperating element carried by the frame.

21. In a grinding apparatus, a frame, a material supporting table movable on the frame, a power means for driving the table in both directions, a reversing mechanism for the power means, adjustable elementsmovable with the table and including aprimarystop and a secondary stop, a primary and a secondary-member mounted on the frame forselective. cooperation.

wherein the cooperation of the primary stop and primary member stops table movement prior to the operation of the difierential.

23. A construction as defined in claim 21, wherein the cooperation of the-secondary stop and secondary member operates the reversing shaft prior to complete stoppage of the table.

interrupting the effective influence of the power train on the member at any selected point in the travel of the member in either direction, said interruption completely stopping member movement without interfering with continued powertrain operation, means for reversing movement of the power train, and means actuated by the continued operation of the power train following complete stopping of member movement to operate the reversing means.

2'7. A machine including a continuous unidirectional power means, a power train operated by the power means, means for reversing the driving effect of the power means on the power train, a member operated by the power train ina direction determined by the particular direction of 30 power-train movement, means for selectively and completely stopping member movement in any one particular direction, the power train continuing in operation following complete stopping of the member, and means responsive to such con-.

35 tinued operation of the power train to automatically operate the reversing means to change direction of power train and its driving effect on the member.

JOHN E. POORMAN. 

